So here's the story:
I bought a 07 G35 sedan about 7 months ago with 80k miles, it currently has 83,6XX miles.

A couple months ago I noticed some weird issue with the car. It seemed like when I let off the gas, the revs dropped instantly, and the car seemed to shift extremely slowly from 1st to 2nd. I had a 2 month vacation so I let the car sit, and when I came back the issue was worse.

So if I'm driving at around 20 MPH and I let off the pedal, it instantly drops in RPM and the car slows down. It's also jerky if I'm not 100% smooth on the pedal. Another weird thing is if I put it in Manual Mode, and stick it in 1st gear, it will rev up and down from 1000 to 1500... on it's own.

It idles perfectly fine, and it seems fine past 3rd gear.

So I checked the transmission fluid, and it was filled wayyy past the max line. The color of the fluid was a light brown color, so it needs to be replaced anyways, but why would it be filled so far past the max line?

Any help would be appreciated.

 

"With the gearshift in Neutral or Park and the parking brake on, let your engine run. Be sure the engine is warm when you pull out the dipstick. (Don’t turn off the engine.)"

Is your engine running?

 

Do a drain and fill, see what happens.

 

Normally the trans fluid being fill passed the max line isn't normally the problem. You should only measure the fluid level after it has warmed up for 5-10 min and while it is in neutral or park.

If I were to guess, the previous owner probably though they needed to add some and didnt know how to measure it.

When the trans fluid is burned it will smell awful from all the slipping. If it keeps slipping you probably need to replace the trans or have it rebuilt.

Hoping that isn't the case for you, but 9 times out of 10...

 

Alright so I guess I'm blind or something, because i checked it again today, and it was right in the middle between the min and max line. So the level is good, but the color is light brown. Should I change it?

Also how hard is it to DIY? I tried to find some Nissan Matic S ATF but I could only find Matic J

 

Well I drained the fluid and changed it, and it didn't really help at all.

The car takes a while to get from 1st to 2nd, and also when you let off the gas it instantly goes down to idle.